The Republican Party's 2012 presidential candidate, former Massachusetts Gov. Mitt Romney, who has repeatedly ruled out another White House run, has added in a radio interview the proviso, "circumstances can change."

Interviewed on The Hugh Hewitt Show, Romney said, "Circumstances can change, but I'm just not going to let my head go there." He added, "I had the chance of running. I didn't win. Someone else has a better chance than I do. And that's what we believe, and that's why I'm not running."

He also raised a hypothetical: "Let's say all the guys that were running all came together and said, 'Hey, we've decided we can't do it, you must do it.' That's the one of a million we're thinking about."

Wisconsin Rep. Paul Ryan, his vice presidential running mate, seemed to encourage another 2016 Romney run. "I sure wish he would," he said on the CBS Sunday program "Face the Nation." "I think he'd make a phenomenal president. He has the intellect, the honor, the character, and the temperament to be a fantastic president. … But he keeps saying that he's not going to run."

Assuming he did not run for president and the party's nominee asked him to become their vice presidential candidate, Hewitt asked, "would you do it?" Romney replied, "I would always be happy to serve my country in any way that I was called upon to do. But that's not a job I would seek. I was seeking the presidency, not the vice presidency," according to the interview transcript.

He also spoke highly of Ryan, describing him as both "brilliant" and "down to earth." Romney said that Ryan "is one of the rare people who knows how to work across the aisle. He's also one of the rare people who works on our side of the aisle effectively."

Among the other Republicans he mentioned as "people who I think have the potential to really ignite interest in our party and potentially win the general" were Govs. Scott Walker of Wisconsin, Bobby Jindal of Louisiana, Chris Christie of New Jersey, and former Florida Gov. Jeb Bush, as well as Sen. Marco Rubio of Florida.